When S1is on and S2,S3,S4,S5 are off, the bulb does not light up at all.
I have not tried the last combination you have suggested with capacitor disconnected. I will try it and update you.
However, based on the feedback by all the readers here, I did following
1. Never switched S1 on and disconnected R1,R2 so as to isolate the hysterisis circuit
2. Connected the load on the Live wire, Neutral wire, MT1, MT2 in 4 different experiments, just to check if the positioning of the load was any way root cause.
The results are still wierd. For one positioning of MT1, MT2, the triac never fired with S1 on, S2 on made bulb light dim, S3 on made the bulb more brighter. When I reversed the Pin1 and Pin2 of triac, the bulb was always on irrespective of S2,S3,S4 positioning.
I observed this pattern for all the 4 different load positioning.
Removing capacitor is something I did not think.
Any idea what would be the resistor value that would fire a BTA12 600B near the peak of each half cycle ?
Note: I am using BTA12 600B and BTA16 600B for my experiments. These are NOT the snubberless version. Do you guys think not having a snubber in my circuit could be the problem. I don't think that is related as I have a simple resistive load, but I am a bit rustic on this now. Also, it would be great if you can point me to an arcticle to design/calculate snubber for my circuit just in case.